1. Field of the Invention
The present invention relates to a drill bit structure, particularly to a drill bit structure having five groove portions, which can drill holes on various workpieces, especially drill micro holes on circuit boards.
2. Description of the Prior Art
Referring to FIG. 1, a conventional drill bit structure is shown. The conventional drill bit 1000 has a bit 1010 and a shank 1100. The bit 1010 has a free end 1012 and a connection end 1016. The connection end 1016 is opposite to the free end 1012 and connected with the shank 1100. The bit 1010 only has two primary groove portions 1020, 1022 both helically extended from the free end 1012 toward the connection end 1016 without overlapping. Further, referring to FIG. 2, the conventional drill bit 1000 is simple-structured. The bit 1010 has two primary cutting portions 1020A, 1022A and two secondary cutting portions 1020B, 1022B, which are formed by the primary groove portions 1020, 1022. The bit 1010 also has two non-overlap chip discharge grooves/flutes, i.e. the two primary groove portions 1020, 1022. However, the two secondary cutting portions 1020B, 1022B, simply formed by the two primary groove portions 1020, 1022, have only a limited drilling/cutting effect. Further, referring to FIG. 3 schematically showing the arrangement/layout of the groove portions of the conventional drill bit 1000, the two non-overlap primary groove portions 1020, 1022 decrease the cross-sectional area of the bit 1010 and hence lower the stiffness of the bit 1010. Consequently, the lower-stiffness drill bit 1000 is unsuitable for high-strength or small-size/micro-size/size-miniaturization drilling processes. Besides, the bit 1010 has a uniform outer diameter, which causes unnecessary friction between the bit 1010 and the wall of the drilled hole, increases resistance of drilling and roughens the surface of the wall.
U.S. Pat. No. 7,018,143B2 disclosed a drill bit structure to overcome the abovementioned problems. The bit of the conventional drill bit structure has a head and a body. The head contacts a workpiece and drills the workpiece. The head has a larger diameter. The body has two primary groove portions/flutes extending from the head for guiding and discharging the chips generated by the drilling of the head. The body also has an annular groove/relief to make the body has a smaller outer diameter than the head so as to decrease the friction between the body of the bit and the drilled hole. Thereby, the quality of the drilled hole is improved.
China Patent No. 101791717B and Japan Patent Publication No. 2007307642A both disclosed a drill bit, which has two primary groove portions/flutes separately extending from the free end and then merged into a single integral chip discharge groove/flute so as to increase the cross-sectional area and stiffness of the bit. However, the merged chip discharge groove has a chip discharge space smaller than the original two separate primary groove portions. In this respect, the prior arts may have a problem of poor chip discharge.
Taiwanese Patent Publication No. 201338896 and China Utility Model No. 202028809U both disclosed a drill bit, which has two primary groove portions/flutes, two secondary groove portions/flutes and a bit annular groove/undercut/relief. The features of the two primary groove portions can be compared to that of China Patent No. 101791717B and Japan Patent Publication No. 2007307642A. The bit groove can be compared to the body groove of U.S. Pat. No. 7,018,143B2. Further, the two secondary groove portions enhance the overall performance of the drill bit. However, the prior arts also have a problem of poor chip discharge.
Although the abovementioned prior arts (Taiwanese Patent Publication No. 201338896, China Utility Model No. 202028809U, China Patent No. 101791717B, Japan Patent Publication No. 2007307642A) are characterized in overlapping two primary groove portions to increase the stiffness of the drill bit, they still have the problem of poor chip discharge. Moreover, the stiffness thereof is still insufficient for high-strength or small-size/micro-size/size-miniaturization drilling process.